Methods and compositions to elicit multivalent immune responses against dominant and subdominant epitopes, expressed on cancer cells and tumor stroma

ABSTRACT

The present invention provides a method of treating cancer by providing to a subject in need thereof an immunogenic composition comprising a nucleic acid construct encoding a polypeptide comprising CTL epitopes PSMA 288-297  and PRAME 425-433 , or a cross-reactive analogue. In embodiments of the present invention there is provided methods and compositions for inducing, entraining, and/or amplifying the immune response to MHC class-I restricted epitopes of carcinoma antigens to generate an effective anti-cancer immune response.

The present application is a continuation application of U.S. patent application Ser. No. 11/454,616, filed on Jun. 16, 2006, which in turn claims the benefit of the filing date of U.S. Provisional Patent Application No. 60/691,579, filed on Jun. 17, 2005, the entirety of each of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention disclosed herein is directed to inducing an MHC class-I restricted immune response and controlling the nature and magnitude of the response, thereby promoting effective immunologic intervention in pathogenic processes. The invention relates to immunogenic compositions that can stimulate a cellular immune response against a target cell. Disclosed herein is an immunogenic composition comprising a nucleic acid construct encoding the CTL epitopes PRAME₄₂₅₋₄₃₃ and PSMA₂₈₈₋₂₉₇ or a cross-reactive analogue of either or both of epitopes. The invention also provides methods of using the described immunogenic composition to elicit a balanced immune response in a subject to whom such compositions are administered.

2. Description of the Related Art

Cancer generally develops when cells in a part of the body continue to grow and divide in an unorderly manner unlike normal cells that grow, divide, and die in an orderly fashion. Although there are many kinds of cancer, they usually start because of out-of-control growth of abnormal cells.

Usual treatment options for cancer include surgery, radiation therapy, and chemotherapy. A fourth branch of treatment is developing, which is referred to as immunotherapy. Immunotherapies attempt to help the immune system recognize cancer cells, and/or to strengthen a response against cancer cells in order to destroy the cancer. Immunotherapies include active and passive immunotherapies. Active immunotherapies attempt to stimulate the body's own immune system to fight the disease. Passive immunotherapies generally do not rely on the body to attack the disease; instead, they use immune system components (such as antibodies) created outside of the patient's body.

Despite various types of cancer treatments, a continuing need exists for additional treatment options. Manipulation of the immune system by use of an anticancer vaccine is one such approach.

To generate a vaccine or other immunogenic composition, an antigen or epitope against which an immune response can be mounted is introduced to a subject. Although neoplastic (cancer) cells are derived from and therefore are substantially identical to normal cells on a genetic level, many neoplastic cells are known to present tumor-associated antigens (TuAAs). In theory, these antigens could be used by a subject's immune system to recognize and attack the neoplastic cells as foreign. Unfortunately, neoplastic cells generally appear to be ignored by the host's immune system.

The immune system can be categorized into two discrete effector arms. The first is innate immunity, which involves numerous cellular components and soluble factors that respond to all infectious challenges. The other is the adaptive immune response, which is customized to respond specifically to precise epitopes from infectious agents. The adaptive immune response is further broken down into two effector arms known as the humoral and cellular immune systems. The humoral arm is centered on the production of antibodies by B-lymphocytes while the cellular arm involves the killer cell activity of cytotoxic T lymphocytes.

Cytotoxic T lymphocytes (CTL) do not recognize epitopes on the infectious agents themselves. Rather, CTL detect fragments of antigens derived from infectious agents that are displayed on the surface of infected cells. As a result antigens are visible to CTL only after they have been processed by the infected cell and thus displayed on the surface of the cell.

The antigen processing and display system on the surface of cells has been well established. CTL recognize short peptide antigens, which are displayed on the surface in non-covalent association with class I major histocompatibility complex molecules (MHC). These class I peptides are in turn derived from the degradation of cytosolic proteins.

In most instances, neoplastic processes evolve to avoid the immune defense mechanisms by employing a range of strategies that result in immune ignorance, tolerance or deviation. Methods that effectively break immune tolerance or repair immune deviation against antigens expressed on cancer cells have been described in the literature (Okano F, et al. J Immunol. 2005, March 1; 174(5):2645-52; Mocellin S, et al., Exp Cell Res. 2004 Oct. 1; 299(2):267-78; Banat G A, et al., Cancer Immunol Immunother. 2001 January; 49(11):573-86) and despite their association with significant levels of systemic immunity, rarely result in reduction of tumor burden. Significant limiting factors impacting this process are sub-optimal trafficking, local activation and/or activity of anti-tumoral effector cells. In fact, it has been shown in most instances that the intra-tumoral presence of immune cells is a rare occurrence—compared to that associated with inflammatory processes such as organ rejection, infections or autoimmune syndromes.

The immune response resulting from exposure to antigens (in a natural context or upon vaccination) that encompass multiple epitopes is inherently associated with a hierarchy relative to the magnitude of the immune response against different, individual epitopes. This occurs in the case of T cell epitopes such as MHC class I and class II restricted epitopes, where dominance and subdominance has been well documented. Dominant epitopes are those that elicit prominent and specific expansions of T cells; whereas subdominant epitopes elicit relatively reduced responses characterized by a limited expansion of specific T cells with diminished functionality.

There are multiple reasons for an immune response to focus on a subset of epitopes within an antigen, regardless of whether the antigen is natural or engineered. These reasons include but are not limited to the following: efficacy of generation of certain peptides or polypeptide precursors within proteasomes (for class I restricted) or endosomes (for class II restricted); their selective transport via TAP (for class I peptides) and alternative mechanisms to compartments where loading onto MHC occurs; their affinity for MHC molecules relative to chaperones or the invariant polypeptide chain that occupies the peptide-binding cleft of nascent MHC molecules and relative to other competing peptides resulting from processing of the same or alternative substrates; the stability of the resulting MHC-peptide complex; and the functionality of T cell repertoire.

In addition, two or more epitopes from different antigens brought together on the same artificial molecule assume a dominant/subdominant relationship due to their intrinsic properties (such as those described above). This limits the practical applicability of composite molecules for the purpose of immunotherapy, particularly when co-targeting of cancer cells (neoplastic) and stromal elements (such as neovasculature) is pursued.

SUMMARY OF THE INVENTION

To amplify immune mediated control of tumoral processes, embodiments of the present invention provide immune mediated attack of neovasculature, in addition to direct attack on tumor cells, as a component of a bi- or multi-valent vaccine strategy aimed at establishing an inflammatory environment within the tumor resulting in shrinkage, stabilization or diminution of growth rate and invasion (local or systemic). This methodology can be more effective in controlling tumor processes than strategies that target either cancer cells or the neovasculature alone and has beneficial implications in regard to therapeutic index (efficacy/safety).

Some embodiments relate to methods and compositions that modulate the immune responses against epitopes with different intrinsic immune properties (e.g. dominant versus subdominant status in a given immunization context), in a manner consistent with increasing the relative activity of subdominant epitopes to achieve co-induction of balanced immune responses against multiple epitopes. This invention is useful when co-targeting multiple antigens such as those expressed by cancer cells and/or underlying stroma.

In some embodiments, co-targeting of tumor neovasculature and cancerous cells, or of multiple antigens on cancer cells, can be achieved by immunotherapeutic compositions comprising expression vectors such as plasmids that elicit immunity against transformed cells, tumor cells and endothelial cells of the neovasculature. Design of plasmids in a “string of beads” format is accomplished as disclosed in U.S. Patent Publication Application No. 20030228634, entitled “EXPRESSION VECTORS ENCODING EPITOPES OF TARGET-ASSOCIATED ANTIGENS AND METHODS FOR THEIR DESIGN” and herein incorporated by reference in its entirety. A preferred embodiment is a bivalent plasmid comprising immunogenic elements derived from molecule(s) expressed on cancer cells and molecule(s) expressed on neovasculature. In particular embodiments of the invention, such molecules correspond to the PRAME and PSMA epitopes and cross-reactive analogues thereof.

In another embodiment, vectors such as plasmids express immunogenic elements derived from molecules co-expressed by cancer cells and neovasculature. In yet another embodiment, vectors such as plasmids express immunogenic elements derived from a receptor and its ligand, where either the receptor or ligand is expressed by the neovasculature, and cancer cells express the other.

In still another embodiment, vectors encode immunogenic components from molecules expressed by cancer cells or neovasculature (or other stromal cells) along with biological response modifiers, including modifiers that act via antigen receptors on B and T cells and those that do not.

In some embodiments, vectors can be administered in a chronological sequence with other immunogenic agents—such as peptides—for the purpose of amplifying or modulating the therapeutic activity against cancer cells, neovasculature or both (disclosed in U.S. Patent Application Publication No. 20050079152 entitled “METHODS TO CONTROL MHC CLASS I-RESTRICTED IMMUNE RESPONSE”; U.S. Provisional Patent Application No. 60/640,402, filed Dec. 29, 2004, and U.S. Publication No. 20060165711, all entitled METHODS TO ELICIT, ENHANCE, AND SUSTAIN IMMUNE RESPONSE AGAINST MHC CLASS I-RESTRICTED EPITOPES, FOR PROPHYLACTIC OR THERAPEUTIC PURPOSES; and U.S. Provisional Application No. 60/691,581 filed on Jun. 17, 2004, entitled MULTIVALENT IMMUNOTHERAPEUTICS FOR CARCINOMA, and U.S. patent application Ser. No. 11/455,279, entitled MUTLIVALENT IMMUNOTHERAPIES FOR CARCINOMA, filed on date even with this application both entitled, each of which is herein incorporated by reference in its entirety) and balancing the response against subdominant and dominant epitopes.

Inducing immune responses to epitopes that are “subdominant” in context of a native antigen provides benefit in treating cancer since such epitopes can be involved in negative selection (central or peripheral) occurring in diseased individuals. Thus, constructs encompassing multiple copies of a subdominant epitope can be used to induce an increased response against such an epitope while preserving immunity against dominant ones.

In addition, effective co-induction of immune responses against epitopes from different antigens presented by the same molecule can offer a more practical approach to generate immunity against multiple antigens. This has direct implications for treatment and prevention of tumoral and infectious diseases.

Overall, broader immune responses achieved by such methods and compositions are more effective in dealing with pathogenic processes as opposed to immune responses heavily dominated by a limited number of specificities. In addition, practicality of multivalent vectors in such methods and compositions can alleviate the need to use numerous components and cumbersome administration protocols to achieve balanced, multivalent responses.

Some embodiments relate to bivalent plasmids expressing PRAME and PSMA epitope sequences (such as those disclosed in the U.S. Patent Application Publication Nos. 20030220239, 20050221440, 20050142144 and PCT Patent Publication No. PCT/US/11101 entitled “EPITOPE SEQUENCES” herein each incorporated by reference in its entirety) and methods of use of these compositions, individually or in combination with other plasmids, to elicit a balanced immune response. Such methods can include an initiating or entraining step wherein the composition can be delivered to various locations on the animal, but preferably is delivered to the lymphatic system, for example a lymph node. The entrainment step can include one or more deliveries of that composition, for example, spread out over a period of time or in a continuous fashion over a period of time.

The methods can further include an amplification step comprising administering a composition comprising a peptide immunogen, having substantial similarity or functional similarity to the corresponding epitopes encoded by the nucleic acid composition. For example, the immunogen can be a cross reactive sequence of the corresponding epitope. The amplification step can be performed one or more times, for example, at intervals over a period of time, in one bolus, or continuously over a period of time. Although not required in all embodiments, some embodiments can include the use of compositions that include an immunopotentiator or adjuvant.

It has been observed that by using this type of immunization protocol that not only can the plasmid initiate an immune response, it biases the response and its subsequent amplification toward an effector as opposed to a regulatory character. Without this prior nucleic acid-based immunization, the repeated administration of peptide leads to a response ever more dominated by regulatory T cells. The long-lived bias toward an effector response is termed entrainment.

Further embodiments include those in which the disclosed plasmids are used individually or in any combination. The peptide compositions corresponding to these epitopes and used in the amplification portion of the immunization strategy can be native sequences or peptide analogs substantially similar or functionally similar to the native epitope sequence. The peptides can be incorporated into the amplification protocol individually or in combinations of 2, 3, or 4 of the immunogens. Reasons for using less than all peptide epitopes include but are not limited to the following: 1) sub-optimal expression of any of the antigens; 2) the patient does not express, or no longer expresses the corresponding antigen; 3) a less robust response is being generated to one or another of the epitopes, in which case such peptide(s) can be given in the absence of the others in order to obtain a more balanced response; and 4) a peptide can be discontinued if it is generating some sort of immunotoxicity.

Additional embodiments relate to methods of modulating the immune response by changing the relative number of immunogen epitopes within a nucleic acid composition. These embodiments can also encompass changing the intrinsic immunogenicity of the immunogen, for example, by encoding amino acid substitutions within the immunogen epitope.

Embodiments additionally can encompass methods of modulating the immune response by selective up-regulation by peptide boost. The peptide compositions corresponding to this amplification step can be native sequences or peptide analogs substantially similar or functionally similar to the native epitope sequence. The selective up-regulation can be achieved by administration of the peptide corresponding to the subdominant epitope in order to obtain a balanced immune response.

Still other embodiments include plasmids that encode an analogue of either the PSMA or PRAME epitopes. Further embodiments can include different epitopes (such as those disclosed in U.S. Patent Application Publication Nos. 20030220239 and 20040180354 both entitled “EPITOPE SEQUENCES” and herein incorporated by reference in their entirety) and analogues substituted in similar combination as the epitopes expressed in the RP8 and RP12 plasmids and corresponding peptide immunogens (such as those disclosed in U.S. Provisional Patent Application No. 60/691,889 entitled “EPITOPE ANALOGUES”, filed on Jun. 17, 2005, and herein incorporated by reference in its entirety) administered as the amplification portion of the immunization strategy.

Some embodiments relate to nucleic acid constructs encoding a polypeptide that includes one or more copies of CTL epitope PSMA₂₈₈₋₂₉₇ (SEQ ID NO:6) and one or more copies of CTL epitope PRAME₄₂₅₋₄₃₃ (SEQ ID NO:5), or a cross-reactive analogue comprising 1-3 substitutions of one or both of the epitopes, wherein the polypeptide does not include a whole antigen. The one or both epitopes can be encoded within a liberation sequence, for example. The polypeptide further can include a sequence encoding one or more epitope clusters. The nucleic acid construct can include a PRAME epitope cluster, for example, amino acid 422-509 of PRAME (SEQ ID NO:21). The nucleic acid construct can include a PSMA epitope cluster, for example, one or more epitope clusters can be amino acids 3-45 (SEQ ID NO:22) or 217-297 of PSMA (SEQ ID NO:23). The PSMA epitope analogue can contain a I297V substitution, for example. The nucleic acid construct further can include one or more of a nuclear import sequence, a promoter (for example, a cytomegalovirus (CMV) promoter), a poly-A sequence, or one or more of a CpG immunostimulatory motifs. The liberation sequence of both the PRAME and PSMA epitopes can be located, for example, in the N-terminal portion of the encoded polypeptide. The encoded polypeptide can be, for example, SEQ ID NO:2. The liberation sequence of both the PRAME and PSMA epitopes can be located, for example, in the C-terminal portion of the encoded polypeptide. For example, the encoded polypeptide can be SEQ ID NO:4.

Some embodiments relate to immunogenic compositions that include a nucleic acid construct described above and elsewhere herein.

Some embodiments relate to methods of treating an individual having cancer, the methods can include the step of administering a therapeutically effective amount of a nucleic acid construct described above and elsewhere herein. The nucleic acid construct can be administered intranodally, for example. The individual can have a cancer that expresses PRAME (SEQ ID NO:20), PSMA (SEQ ID NO:19), or both in neoplastic cells or tumor-associated neovasculature cells.

Some embodiments relate to methods of treating an individual having cancer. The methods can include the steps of administering an effective amount of the nucleic acid construct described above and elsewhere herein to induce an immune response; and amplifying the immune response by boosting with at least one peptide analogue corresponding to an epitope encoded by the nucleic acid construct. The individual can have, for example, a cancer that expresses PRAME on cancer cells and PSMA on tumor-associated vasculature cells. The individual can have a cancer that expresses PRAME, PSMA, or both in neoplastic cells or tumor-associated neovasculature cells.

Some embodiments relate to use of an immunogenic composition or nucleic acid construct as described above and elsewhere herein in the preparation of a medicament for the treatment of an individual having cancer. The medicament can be for the treatment of an individual having cancer by administering the medicament intranodally. The individual can have a cancer that expresses PRAME, PSMA, or both in neoplastic cells or tumor-associated neovasculature cells.

Some embodiments relate to the use of an immunogenic composition or a nucleic acid construct as described above and elsewhere herein in the preparation of a medicament for use in the inducing an immune response targeting of tumor associated neovasculature. For example, the tumor-associated vasculature cells displays PRAME.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Structure of two monovalent plasmids and one bivalent plasmid.

FIG. 2. ⁵¹Cr-release assay depicting the % specific cell lysis in cells expressing the P2, R2, and RP5 plasmids. Data are presented as follows: the x-axis shows target cells used with different effector to target ratio; the y-axis shows the corresponding percentage specific lysis.

FIG. 3. Structure of additional plasmids designed expressing both PRAME and PSMA epitopes. Structure of the monovalent PRAME plasmid R2 is depicted. P2 represents the monovalent PSMA plasmid.

FIG. 4. ELISpot analysis of PRAME and PSMA depicting induction of bivalent responses achieved by plasmids encompassing epitopes from the different antigens depicted in FIG. 3. Animals were immunized with 2 injections of PRAME/PSMA bivalent plasmid (1 mg/ml) in bilateral lymph nodes. 5×10⁵ isolated splenocytes were incubated with 10 μg PSMA₂₈₈₋₂₉₇ (SEQ ID NO:6): natural peptide or 10 μg PRAME₄₂₅₋₄₃₃ (SEQ ID NO:5) natural peptide for 42 hours prior to development. Graphs represent average +/−SEM.

FIG. 5. Tetramer analysis of PRAME and PSMA following RP12 bivalent plasmid immunization. The data shows a bivalent immune response to PRAME and PSMA with relative dominance of the response against the PRAME epitope in plasmid-only primed mice.

FIGS. 6-6B. Tetramer analysis of PRAME and PSMA in mice receiving RP12 or RP8 bivalent plasmid immunization followed by a PSMA₂₈₈₋₂₉₇ (I297V) (SEQ ID NO:7) peptide analogue boost (FIG. 6). Tetramer analysis of PRAME and PSMA in individual animals following RP12 or RP8 bivalent plasmid immunization and PSMA₂₈₈₋₂₉₇ (I297V) (SEQ ID NO:7) peptide analogue boost (FIG. 6B).

FIG. 7. ELISpot analysis in animals primed with RP12 or RP8 and boosted with PSMA₂₈₈₋₂₉₇ (I297V) (SEQ ID NO:7) and PRAME₄₂₅₋₄₃₃ (L426Nva, L433Nle) (SEQ ID NO:30) peptide analogues.

FIG. 8. Polypeptide sequence for RP8 (SEQ ID NO:2).

FIG. 9. Polypeptide sequence for RP12 (SEQ ID NO:4).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiments relate to compositions that can elicit multivalent immune responses against dominant and subdominant epitopes. Some embodiments also relate to methods of designing the composition by: selecting antigens that are expressed by cancer cells and/or stromal (neovasculature) cells; defining epitopes that can have different intrinsic immune properties, that constitute valid immune targets on such cancer or stromal cells; and modulating the relative number of dominant and subdominant epitopes within a certain molecule (such as a therapeutic vector) by decreasing the ratio between the number of dominant and subdominant epitopes, while providing optimal flanking residues for appropriate generation within processing compartments.

Additional methods are described such as replacing one or multiple copies of subdominant epitopes with analogue sequences or preferentially positioning epitopes within the molecule to modify the relative immunogenicity of such epitopes and ensure a more balanced, multivalent response. Testing for efficacy can follow the design of a set of candidate epitopes. Use of such molecules can be complemented by selective amplification of responses against subdominant epitopes, in the context of prime-boost immunization strategies.

The general method for vaccine design can involve utilizing a defined algorithm that starts with a natural or artificial sequence to find the correct ratio of dominant and subdominant epitopes for plasmids, vectors, and molecules encompassing multiple copies of dominant and subdominant epitopes; engineering a set of compounds; in vitro and in vivo characterization steps; and selection of appropriate plasmids or other vectors eliciting the desired balanced immune response.

An epitope as referred to herein, is a molecule or substance capable of stimulating an immune response. In preferred embodiments, epitopes according to this definition include but are not necessarily limited to a polypeptide and a nucleic acid encoding a polypeptide, wherein the polypeptide is capable of stimulating an immune response. In other preferred embodiments, epitopes according to this definition include but are not necessarily limited to peptides presented on the surface of cells, the peptides being non-covalently bound to the binding cleft of class I MHC, such that they can interact with T cell receptors.

An MHC epitope as referred to herein is a polypeptide having a known or predicted binding affinity for a mammalian class I or class II major histocompatibility complex (MHC) molecule.

An immune epitope referred to herein, is a polypeptide fragment that is an MHC epitope, and that is displayed on a cell in which immune proteasomes are predominantly active. In another preferred embodiment, an immune epitope is defined as a polypeptide containing an immune epitope according to the foregoing definition, which is flanked by one to several additional amino acids. In another preferred embodiment, an immune epitope is defined as a polypeptide including an epitope cluster sequence, having at least two polypeptide sequences having a known or predicted affinity for a class I MHC. In yet another preferred embodiment, an immune epitope is defined as a nucleic acid that encodes an immune epitope according to any of the foregoing definitions.

SUBSTANTIAL SIMILARITY—this term is used to refer to sequences that differ from a reference sequence in an inconsequential way as judged by examination of the sequence. Nucleic acid sequences encoding the same amino acid sequence are substantially similar despite differences in degenerate positions or modest differences in length or composition of any non-coding regions. Amino acid sequences differing only by conservative substitution or minor length variations are substantially similar. Additionally, amino acid sequences comprising housekeeping epitopes that differ in the number of N-terminal flanking residues, or immune epitopes and epitope clusters that differ in the number of flanking residues at either terminus, are substantially similar. Nucleic acids that encode substantially similar amino acid sequences are themselves also substantially similar.

FUNCTIONAL SIMILARITY—this term is used to refer to sequences that differ from a reference sequence in an inconsequential way as judged by examination of a biological or biochemical property, although the sequences may not be substantially similar. For example, two nucleic acids can be useful as hybridization probes for the same sequence but encode differing amino acid sequences. Two peptides that induce cross-reactive CTL responses are functionally similar even if they differ by non-conservative amino acid substitutions (and thus do not meet the substantial similarity definition). Pairs of antibodies, or TCRs, that recognize the same epitope can be functionally similar to each other despite whatever structural differences exist. In testing for functional similarity of immunogenicity one would generally immunize with the “altered” antigen and test the ability of the elicited response (Ab, CTL, cytokine production, etc.) to recognize the target antigen. Accordingly, two sequences may be designed to differ in certain respects while retaining the same function. Such designed sequence variants are among the embodiments of the present invention.

I. Plasmid Construction

Some embodiments of the present invention provide a number of plasmids, e.g., pRP8 (SEQ ID NO:1), pRP9, pRP10, pRP11, pRP12 (SEQ ID NO:3), and pRP13, having the ability to elicit or promote a bivalent response against the tumor associated antigens PRAME and PSMA, specifically against the epitopes PRAME₄₂₅₋₄₃₃ (SEQ ID NO:5) and PSMA₂₈₈₋₂₉₇ (SEQ ID NO:6). In particular embodiments of the invention there are provided the plasmids, pRP12 and pRP8 as immunogenic compositions. The methodology for generating plasmid constructs of the invention are as detailed, below.

Plasmid construction in preferred embodiments can entail stepwise ligation of sets of long complementary oligonucleotides resulting in the generation of DNA sequence encoding epitopes arrayed as a “string-of-beads.” These DNAs bear appropriate cohesive ends for restriction enzymes that can be used for further ligation with DNAs encoding epitope cluster regions, which are amplified by performing PCR on cloned cDNA for PSMA or PRAME as a template. The entire insert is then ligated into the vector backbone between Afl II and EcoR I restriction sites. The entire coding sequence is verified by DNA sequencing. PCR-based mutagenesis can be used to generate sequence encoding analogue epitope peptide, or to adjust the copies number of dominant/subdominant epitopes to achieve the desired ratio. The sequences of the two plasmids, RP8 and RP12, are described in detail and disclosed as SEQ ID NO.1 and SEQ ID NO.3. For the specific plasmids described herein, the vector backbone is a modified version of pVAX, by Invitrogen (Carlsbad, Calif.), which has been previously disclosed in U.S. Pat. No. 6,709,844 entitled Avoidance of Undesirable Replication Intermediates in Plasmid Propagation, and U.S. patent application Ser. No. 09/561,572 entitled Expression Vectors Encoding Epitopes of Target-Associated Antigens, each of which is hereby incorporated by reference in its entirety. One of skill in the art will recognize that the coding sequences of the present invention can be placed in any nucleic acid vector suitable for use as a vaccine without exceeding the scope of the invention. For example, the sequences encoding the other mentioned plasmids can be inserted into the same or a similar backbone as used in pRP8 and pRP12 plasmids.

pRP8 and pRP12 are recombinant DNA plasmids that encode one polypeptide with HLA A2-restricted CTL epitopes from PSMA (288-297) (SEQ ID NO:6) and an analogue thereof) and PRAME (425-433) (SEQ ID NO:5). Both polypeptides also include regions comprising epitope clusters of PSMA (3-45) (SEQ ID NO:22), (217-297) (SEQ ID NO:24) and PRAME (422-509) (SEQ ID NO:21). Flanking the defined PSMA and PRAME epitopes are short amino acid sequences optimal for liberation of the epitopes in question by immunoproteasome processing. The coding sequence for the polypeptide in the plasmid is under the control of promoter/enhancer sequence from cytomegalovirus (CMVp), which allows efficient transcription of mRNA for the polypeptide upon uptake by APCs. The bovine growth hormone polyadenylation signal (BGH polyA) at the 3′ end of the encoding sequence provides a signal for polyadenylation of the messenger to increase its stability as well as for translocation out of the nucleus into the cytoplasm for translation. To facilitate plasmid transport into the nucleus after uptake, a nuclear import sequence (NIS) from simian virus 40 (SV40) has been inserted in the plasmid backbone. The plasmid carries two copies of a CpG immunostimulatory motif, one in the NIS sequence and one in the plasmid backbone. Lastly, two prokaryotic genetic elements in the plasmid are responsible for amplification in E. coli, the kanamycin resistance gene (Kan R) and the pMB1 bacterial origin of replication.

A. RP8 Recombinant DNA Plasmid

For RP8, the amino acid sequence of the encoded polypeptide (297 amino acid residues in length; SEQ ID NO:2) contains two liberation sequences, a 17 amino acid substrate at its N-terminus for PRAME₄₂₅₋₄₃₃ (MKRPSIKR-SLLQHLIGL; SEQ ID NO:25) and a 66 amino acid substrate at its C-terminus for PSMA₂₈₈₋₂₉₇ (RK-GLPSIPVHPI-LV-GLPSIPVHPI-KRISPEKEEQYIAKR-GLPSIPVHPI-KRPSIK-RGLPSIPVHPV; SEQ ID NO:8). The entire polypeptide sequence of the encoded immunogen (SEQ ID NO:2) is shown in FIG. 8.

The stretch of the first 8 amino acid residues is an artificial sequence that has been shown to facilitate processing of CTL epitopes by immunoproteasomes. The next 9 amino acids (in italics) are PRAME₄₂₅₋₄₃₃ (SEQ ID NO:5), a potent HLA A2-specific CTL epitope that triggers strong anti-tumor immune responses in both in vitro immunization of human PBMC and in vivo immunization in mice. This PRAME epitope sequence is followed by a segment (amino acid 18-105 of the immunogen) of PRAME₄₂₂₋₅₀₉, comprising two epitope clusters: PRAME₄₂₂₋₄₄₃ (SEQ ID NO:26) and PRAME₄₅₉₋₄₈₇ (SEQ ID NO:27). Two PSMA epitope clusters (in italics), PSMA₃₋₄₅ (SEQ ID NO:22) (amino acid 108-150) and PSMA₂₁₇₋₂₉₇ (SEQ ID NO:24) (amino acid 151-231), are placed after the PRAME epitope cluster. These and other PRAME and PSMA epitope clusters have been disclosed in U.S. patent application Ser. Nos. 10/117,937, 11/067,064, and 11/067,159, each entitled Epitope Sequences and each of which is hereby incorporated by reference in its entirety. These epitope clusters contain a number of predicted HLA A2-specific epitopes and thus can be useful in generating a response to immune epitopes (described in U.S. Patent Application Publication No. 20030215425 entitled EPITOPE SYNCHRONIZATION IN ANTIGEN PRESENTING CELLS and U.S Patent Application Publication Nos. 20030228634; 20040132088; and 20040203051, entitled EPITOPE CLUSTERS, each of which is hereby incorporated by reference in its entirety). A “string-of-beads” epitope array with multiple copies of PSMA₂₈₈₋₂₉₇ (GLPSIPVHPI (SEQ ID NO:6); in boldface) constitutes the rest of the polypeptide (amino acid 232-297). Four copies of PSMA₂₈₈₋₂₉₇ are incorporated with the last copy being an analogue (GLPSIPVHPV; SEQ ID NO:7). Both the native PSMA₂₈₈₋₂₉₇ and its analogue have been shown to induce significant CTL responses in both in vitro immunization of human PBMC and in vivo immunization in mice with the analogue displaying elevated MHC class I binding and immunogenicity. Between PSMA₂₈₈₋₂₉₇ epitope sequences are short amino acid sequences designated to be “cleavage helper sequences” to facilitate the processing and liberation of the epitope. These two epitopes are thus encoded in such a manner that they can be expressed, processed, and presented by pAPCs.

B. RP12 Recombinant DNA Plasmid

For the RP12 plasmid, the amino acid sequence of the encoded polypeptide (275 amino acid residues in length; SEQ ID NO:4) contains one amino acid substrate or liberation sequence and a hybrid “string-of-beads” encompassing a substrate at its C-terminus for the liberation of both the PRAME and PSMA epitopes. The entire polypeptide sequence of the encoded immunogen is shown in FIG. 9. The liberation sequence represented as SEQ ID NO:9 is as follows: KR-SLLQHLIGL-GDAAY-SLLQHLIGL-ISPEKEEQYIA-SLLQHLIGL-KRPSIKR-GLPSIPVHPV.

Segments of amino acid 2-44, 45-126, and 127-213 of the encoded immunogen are epitope clusters joined one to the next: PSMA₃₋₄₅ (SEQ ID NO:22), PSMA₂₁₇₋₂₉₇ (SEQ ID NO:23), and PRAME₄₂₂₋₅₀₉ (SEQ ID NO:21), respectively. In the “string-of-beads” hybrid substrate, there are 3 copies of PRAME₄₂₅₋₄₃₃ (SLLQHLIGL; in boldface; SEQ ID NO:5) and one copy of PSMA₂₈₈₋₂₉₇ analogue (GLPSIPVHPV; in sans serif boldface; SEQ ID NO:7) at the C-terminus of the polypeptide. Between the PRAME₄₂₅₋₄₃₃ and PSMA₂₈₈₋₂₉₇ epitope sequences are the short amino acid sequences designated to be “cleavage helper sequences” to facilitate processing and liberation of the epitopes. These two epitopes are thus encoded in such a manner that they can be expressed, processed, and presented by pAPCs.

Further details on the RP12 plasmid are disclosed in U.S. Provisional Patent Application No. 60/691,579, filed on Jun. 17, 2005, entitled METHODS AND COMPOSITIONS TO ELICIT MULTIVALENT IMMUNE RESPONSES AGAINST DOMINANT AND SUBDOMINANT EPITOPES, EXPRESSED ON CANCER CELLS AND TUMOR STROMA, incorporated herein by reference in its entirety. All other plasmids were constructed in a similar fashion using the methodology as applied to RP8 and RP12. The plasmid R2, also referred to as pCTLR2, is disclosed in the Examples. The P2 plasmid as shown in FIGS. 1 and 3, is a monovalent PSMA plasmid. The RP5 plasmid encompasses elements from both P2 and R2.

Various methodologies for constructing or designing plasmids are well established in the art as would be known to the skilled artisan. Such methodologies are described in many references, such as, for example, Molecular Cloning, Sambrook J and Russell D. W., CSHL Press, (2001), specifically incorporated herein by reference.

In constructing the nucleic acids encoding the polypeptide epitopes of the invention, the gene sequence of the associated tumor associated antigen (e.g., PRAME and PSMA) can be used, or the polynucleotide can be assembled from any of the corresponding codons. For a 10 amino acid epitope this can constitute on the order of 10⁶ different sequences, depending on the particular amino acid composition. While large, this is a distinct and readily definable set representing a miniscule fraction of the >10¹⁸ possible polynucleotides of this length, and thus in some embodiments, equivalents of a particular sequence disclosed herein encompass such distinct and readily definable variations on the listed sequence. In choosing a particular one of these sequences to use in a vaccine, considerations such as codon usage, self-complementarity, restriction sites, chemical stability, etc. can be used as will be apparent to one skilled in the art.

An epitope cluster as contemplated in the present invention is a polypeptide, or a nucleic acid sequence encoding it, that is a segment of a native protein sequence comprising two or more known or predicted epitopes with binding affinity for a shared MHC restriction element, wherein the density of epitopes within the cluster is greater than the density of all known or predicted epitopes with binding affinity for the shared MHC restriction element within the complete protein sequence. Epitope clusters and their uses are described in U.S. Patent Application Publication Nos. 20030220239, 20050221440, 20050142144; 20030215425, 20030228634, 20040132088, 20040203051 and PCT Patent Application Publication No. PCT/US/11101; all of which are incorporated herein by reference in their entirety.

A substrate or liberation sequence as employed in the present invention, is a designed or engineered sequence comprising or encoding a PRAME and/or PSMA epitope embedded in a larger sequence that provides a context allowing the PRAME and/or PSMA epitope to be liberated by immunoproteasomal processing, directly or in combination with N-terminal trimming or other processes.

The following are additional examples of encoded polypeptide sequences that can be used in some embodiments, for example, they can be encoded by the various plasmids or used in the methods, etc.

R2 (SEQ ID NO: 10) MALQSLLQHLIGLSNLTHVLYPVPLESYEDIHGTLHLERLAYLHARLR ELLCELGRPSMVWLSANPCPHCGDRTFYDPEPILCPCFMPNKRSLLQH LIGLGDAAYSLLQHLIGLISPEKEEQYIASLLQHLIGLKRPSIKRSLL QHLIGL P2 (SEQ ID NO: 11) MNLLHETDSAVATARRPRWLCAGALVLAGGFFLLGFLFGWFIKSAQLA GAKGVILYSDPADYFAPGVKSYPDGWNLPGGGVQRGNILNLNGAGDPL TPGYPANEYAYRRGIAEAVGLPSIPVHPIRKGLPSIPVHPILVGLPSI PVHPIKRISPEKEEQYIAKRGLPSIPVHPIKRPSIKRGLPSIPVHPI RP5 (SEQ ID NO: 12) MISPEKEEQYIASLLQHLIGLKRSLLQHLIGLKRPSIKRSLLQHLIGL ALQSLLQHLIGLSNLTHVLYPVPLESYEDIHGTLHLERLAYLHARLRE LLCELGRPSMVWLSANPCPHCGDRTFYDPEPILCPCFMPNKLNLLHET DSAVATARRPRWLCAGALVLAGGFFLLGFLFGWFIKSAQLAGAKGVIL YSDPADYFAPGVKSYPDGWNLPGGGVQRGNILNLNGAGDPLTPGYPAN EYAYRRGIAEAVGLPSIPVHPIRKGLPSIPVHPILVGLPSIPVHPIKR ISPEKEEQYIAKRGLPSIPVHPIKRPSIKRGLPSIPVHPI RP9 (SEQ ID NO: 14) MISPEKEEQYIASLLQHLIGLKRPSIKRSLLQHLIGLALQSLLQHLIG LSNLTHVLYPVPLESYEDIHGTLHLERLAYLHARLRELLCELGRPSMV WLSANPCPHCGDRTFYDPEPILCPCFMPNKLNLLHETDSAVATARRPR WLCAGALVLAGGFFLLGFLFGWFIKSAQLAGAKGVILYSDPADYFAPG VKSYPDGWNLPGGGVQRGNILNLNGAGDPLTPGYPANEYAYRRGIAEA VGLPSIPVHPIRKGLPSIPVHPILVGLPSIPVHPVKRGLPSIPVHPVK RPSVKRGLPSIPVHPV RP 10 (SEQ ID NO: 15) MISPEKEEQYIASLLQHLIGLALQSLLQHLIGLSNLTHVLYPVPLESY EDIHGTLHLERLAYLHARLRELLCELGRPSMVWLSANPCPHCGDRTFY DPEPILCPCFMPNKLNLLHETDSAVATARRPRWLCAGALVLAGGFFLL GFLFGWFIKSAQLAGAKGVILYSDPADYFAPGVKSYPDGWNLPGGGVQ RGNILNLNGAGDPLTPGYPANEYAYRRGIAEAVGLPSIPVHPIRKGLP SIPVHPILVGLPSIPVHPVKRGLPSIPVHPVKRPSVKRGLPSIPVHPV RP11 (SEQ ID NO: 16) MKRSLLQHLIGLKRPSIKRSLLQHLIGLALQSLLQHLIGLSNLTHVLY PVPLESYEDIHGTLHLERLAYLHARLRELLCELGRPSMVWLSANPCPH CGDRTFYDPEPILCPCFMPNKLNLLHETDSAVATARRPRWLCAGALVL AGGFFLLGFLFGWFIKSAQLAGAKGVILYSDPADYFAPGVKSYPDGWN LPGGGVQRGNILNLNGAGDPLTPGYPANEYAYRRGIAEAVGLPSIPVH PIRKGLPSIPVHPVLVGLPSIPVHPVKRISPEKEEQYIAKRGLPSIPV HPIKRPSIKRGLPSIPVHPV RP13 (SEQ ID NO: 18) MKRSLLQHLIGLKRPSIKRSLLQHLIGLALQSLLQHLIGLSNLTHVLYP VPLESYEDIHGTLHLERLAYLHARLRELLCELGRPSMVWLSANPCPHCG DRTFYDPEPILCPCFMPNKLNLLHETDSAVATARRPRWLCAGALVLAGG FFLLGFLFGWFIKSAQLAGAKGVILYSDPADYFAPGVKSYPDGWNLPGG GVQRGNILNLNGAGDPLTPGYPANEYAYRRGIAEAVGLPSIPVHPVLVG LPSIPVHPVKRISPEKEEQYIAKRGLPSIPVHPIKRPSIKRGLPSIPVH PV

II. Immunogenic Compositions of the Present Invention

The present invention contemplates the use of multiple molecules expressed by cancer cells and by the neovasculature as therapeutic targets in the treatment of cancer by active immunotherapy. Such molecules include tumor-associated antigens (TuAAs) which are antigens expressed by the cancer cell itself or associated with non-cancerous components of the tumor, such as tumor-associated neovasculature or other stroma. Determination of TuAA expression profiles can help to match a patient's cancer condition or type with an appropriate immunotherapeutic agent or regimen. In particular embodiments, epitopes of the tumor associated antigens PRAME and PSMA are employed in designing bivalent plasmids that can elicit a strong immune response in a subject to whom such plasmid are administered as a cancer therapeutics. Cross-reactive analogues of PRAME and PSMA are also contemplated in the embodiments of the present invention.

The tumor associated antigen PRAME (SEQ ID NO:20), employed in the present invention, is also known as MAPE, DAGE, and OIP4. PRAME is known in the art as a cancer-testis (CT) antigen. However, unlike many CT antigens, such as: MAGE, GAGE and BAGE, it is expressed in acute myeloid leukemias. PRAME as a TuAA is disclosed in U.S. Pat. No. 5,830,753, incorporated herein by reference in its entirety. In preferred embodiments, the present invention provides epitopes of PRAME and analogues thereof.

Another TuAA employed in the present invention is the prostate-specific membrane antigen (PSMA) (SEQ ID NO:19). PSMA is found to be highly expressed in prostate cancer cells. However, PSMA expression is also noted in normal prostate epithelium and in the neovasculature of non-prostatic tumors. PSMA as an anti-neovasculature preparation is disclosed in U.S. Provisional Patent Application No. 60/274,063, and U.S. Patent Publication Application Nos. 20030046714 and 20050260234; each of which is incorporated herein by reference in its entirety. PSMA as a TuAA is described in U.S. Pat. No. 5,538,866 incorporated herein by reference in its entirety. In preferred embodiments, the present invention provides epitopes of PSMA and analogues thereof.

Cross-reactive analogue as used herein may refer to a peptide comprising 1-3 amino acid substitutions, and/or one amino acid deletion or addition as compared to the native peptide sequence that induces effector function (e.g., cytolysis or cytokine secretion) distinguishable from background, from a CTL reactive with the native peptide. In preferred embodiments effector function is at least 30, 50, 60, 70, or 80% of that induced by the native peptide.

In some embodiments of the present invention, peptides comprising the native sequence or analogues (cross-reactive) of PRAME and PSMA may also be administered as a peptide boost in combination with the plasmids of the invention. Native peptide sequences and peptide analogues of PRAME and PSMA, are disclosed in U.S. Patent Application No. 20060057673 and U.S. Provisional Patent Application No. 60/691,889, each of which is hereby incorporated by reference in its entirety. The peptide analogues, PRAME₄₂₅₋₄₃₃ L426Nva, L433Nle (SEQ ID NO:30) and PSMA₂₈₈₋₂₉₇ I297V (SEQ ID NO:7) are described in U.S. Provisional Application No. 60/580,962; U.S. patent application Ser. No. 11/155,929; U.S. Provisional Application No. 60/581,001; U.S. patent application Ser. No. 11/156,253; U.S. patent application Ser. No. 11/156,369 U.S. Provisional Patent Application No. 60/691,889, U.S. patent application Ser. No. 11/455,278, entitled PRAME PEPTIDE ANALOGUES, U.S. patent application Ser. No. 11/454,633, entitled PSMA PEPTIDE ANALOGUES, and U.S. patent application Ser. No. 11/454,300, entitled MELANOMA ANTIGEN PETIDE ANALOGUES each of which is hereby incorporated by reference in its entirety.

As discussed above, some embodiments relate to immunogenic compositions for the treatment of cancer comprising plasmids encoding CTL epitopes of PRAME and PSMA and cross-reactive analogues thereof. Such an immunogenic composition can elicit a robust or strong cell-mediated immune response to target a particular cancer thereby eliminating, eradicating or ameliorating the cancer in a subject.

III. Entraining-and-Amplifying Therapeutics for Administration

In a preferred embodiment, the present invention provides an immunogenic composition comprising a nucleic acid construct encoding the CTL epitopes PRAME₄₂₅₋₄₃₃ (SEQ ID NO:5) and PSMA₂₈₈₋₂₉₇ (SEQ ID NO:6) or a cross-reactive analogue of either or both these epitopes. In some embodiments of the invention a plasmid prime/peptide boost approach may be employed wherein the recombinant DNA plasmid expressing the PRAME and PSMA epitopes may be administered in conjunction with a synthetic peptides such as a PRAME and or PSMA peptide or analogue thereof.

The immunogenic composition of the invention comprising a nucleic acid construct encoding the CTL epitopes PRAME₄₂₅₋₄₃₃ and PSMA₂₈₈₋₂₉₇ or a cross-reactive analogue of one or both epitopes, can be delivered via lymph node injection, directly into the organs where the immune responses are initiated and amplified, according to an optimized immunization schedule. Embodiments of the current invention can be administered to patients with tumor tissue that express HLA-A2, particularly HLA-A*0201. Therefore, the immunogenic composition comprising a plasmid and one or more peptides or analogues thereof can be administered in treating a cancer in a subject. The disclosed embodiments of the present invention relate to entrain-and-amplify therapeutics for cancer that can be used to achieve a bi- or multivalent attack, offering the advantage of increasing the sensitivity of the tumor to attack.

Therefore, in particular embodiments, the present invention provides bivalent entraining-and-amplifying therapeutics for the treatment of cancer. Such bivalent therapeutics can target more than one antigen on a tumor cell. In instances where more than a single antigen on a tumor cell is targeted, the effective concentration of antitumor therapeutic is increased accordingly. Attack on stroma associated with the tumor, such as vasculature, can increase the accessibility of the tumor cells to the agent(s) targeting them. Thus, even an antigen that is also expressed on some normal tissue can receive greater consideration as a target antigen if the other antigens to be targeted in a bi- or multivalent attack are not also expressed by that tissue. The plasmids of the current invention can be used in conjunction with additional plasmids that express other epitopes, and corresponding amplifying peptides, to create therapeutic protocols of higher valency. Exemplary immunogenic products are disclosed in U.S. Provisional Patent Application No. 60/691,581, filed on Jun. 17, 2005 and U.S. patent application Ser. No. 11/455,279, filed on date even with the instant application, each entitled MULTIVALENT ENTRAIN-AND-AMPLIFY IMMUNOTHERAPEUTICS FOR CARCINOMA, and each incorporated by reference in its entirety.

An “entraining” immunogen as contemplated in the present invention includes in many embodiments an induction that confers particular stability on the immune profile of the induced lineage of T cells.

As contemplated in the present invention, the term “amplifying or amplification”, as of a T cell response, includes in many embodiments a process for increasing the number of cells, the number of activated cells, the level of activity, rate of proliferation, or similar parameter of T cells involved in a specific response.

The entrain-and-amplify protocol employed in the present invention is described in greater detail in U.S. Patent Publication No. 20050079152, U.S. Provisional Patent Application No. 60/640,402, and U.S. patent application Ser. No. 11/323,572 each entitled “METHODS TO ELICIT, ENHANCE AND SUSTAIN IMMUNE RESPONSES AGAINST MHC CLASS I-RESTRICTED EPITOPES, FOR PROPHYLACTIC OR THERAPEUTIC PURPOSES” which are incorporated herein by reference in their entirety.

IV. Biological Response Modifiers (BRMS) or Immunopotentiators

In some embodiments, the present invention may further employ a biological response modifier (BRM) or immunopotentiator in conjunction with the immunogenic compositions comprising a recombinant DNA plasmid encoding the CTL epitopes PRAME and PSMA, in eliciting an immune response. The immunopotentiators or BRMs contemplated by the present invention can act in an immunosuppressive or immunostimulatory manner to mediate an immune response. Immunopotentiators or BRMs of the present invention may refer to any molecule that modulates the activity of the immune system, or the cells thereof, through an interaction other than with an antigen receptor. BRMs as contemplated in the present invention may further include natural or synthetic small organic molecules that exert immune modulating effects by stimulating pathways of innate immunity.

In particular embodiments, the present invention also contemplates immunopotentiators or BRMS which may include, but are not limited to, for example: cytokines such as IL-12, IL-18, GM-CSF, flt3 ligand (flt3L), interferons, TNF-alpha, and the like; chemokines such as IL-8, MIP-3alpha, MIP-1alpha, MCP-1, MCP-3, RANTES, and the like. Other examples of BRMs that may be utilized in the present invention are molecules that trigger cytokine or chemokine production, such as ligands for Toll-like receptors (TLRs), peptidoglycans, LPS or analogues, unmethylated CpG oligodeoxynucleotides (CpG ODNs); dsRNAs such as bacterial dsDNA (which contains CpG motifs) and synthetic dsRNA (polyl:C) on APC and innate immune cells that bind to TLR9 and TLR3, respectively. One class of BRM includes mostly small organic natural or synthetic molecules, which exert immune modulating effects by stimulating pathways of innate immunity. Thus, small molecules that bind to TLRs such as a new generation of purely synthetic anti-viral imidazoquinolines, e.g., imiquimod and resiquimod, that have been found to stimulate the cellular path of immunity by binding the TLRs 7 and 8 (Hemmi, H. et al., Nat Immunol 3: 196-200, 2002; Dummer, R. et al., Dermatology 207: 116-118, 2003; each of which is incorporated herein by reference in its entirety) may be employed. BRMs may further include immunopotentiating adjuvants that activate pAPC or T cells including, for example: endocytic-Pattern Recognition Receptor (PRR) ligands, quillaja saponins, tucaresol and the like.

V. Methods of Delivering Compositions of the Present Invention

In the present invention, the preferred administration of the immunogenic composition comprising recombinant DNA plasmids encoding the CTL epitopes PRAME and PSMA, or such plasmids followed by one or more peptide(s) as one or more boost, is via lymph node injection. Other immunization protocols, for example, using plasmid for other than the initiation dose(s), relying on plasmid alone, or utilizing other types of boosting reagents, while less preferred embodiments, are not excluded from the scope of the invention. Embodiments of the present invention encompass bivalent plasmids expressing both of the immunogens PRAME and PSMA. In delivering the immunogenic compositions of the invention to a subject in need thereof, lymph node injection is preferred as it allows for delivery directly into the organs where the immune responses are initiated and amplified according to an optimized immunization schedule.

To introduce the immunogenic composition into the lymphatic system of the patient the composition is preferably directed to a lymph vessel, lymph node, the spleen, or other appropriate portion of the lymphatic system. In some embodiments each component is administered as a bolus. In other embodiments, one or more components are delivered by infusion, generally over several hours to several days. Preferably, the composition is directed to a lymph node such as an inguinal or axillary node by inserting a catheter or needle to the node and maintaining the catheter or needle throughout the delivery. Suitable needles or catheters are available made of metal or plastic (e.g., polyurethane, polyvinyl chloride (PVC), TEFLON, polyethylene, and the like). In inserting the catheter or needle into the inguinal node for example, the inguinal node is punctured under ultrasonographic control using a Vialon™ Insyte W™ cannula and catheter of 24G3/4 (Becton Dickinson, USA) which is fixed using Tegaderm™ transparent dressing (Tegaderm™, St. Paul, Minn., USA). An experienced radiologist generally does this procedure. The location of the catheter tip inside the inguinal lymph node is confirmed by injection of a minimal volume of saline, which immediately and visibly increases the size of the lymph node. The latter procedure allows confirmation that the tip is inside the node. This procedure can be performed to ensure that the tip does not slip out of the lymph node and can be repeated on various days after implantation of the catheter.

The therapeutic composition(s) of the present invention may be administered to a patient in a manner consistent with standard vaccine delivery protocols that are well known to one of ordinary skill in the art. Methods of administering immunogenic compositions of the present invention comprising plasmids and peptides or peptide analogues of the TuAAs PRAME and PSMA include, without limitation, transdermal, intranodal, perinodal, oral, intravenous, intradermal, intramuscular, intraperitoneal, and mucosal administration, delivery by injection or instillation or inhalation. A particularly useful method of vaccine delivery to elicit a CTL response is disclosed in Australian Patent No. 739189; U.S. Pat. Nos. 6,994,851 and 6,977,074 both entitled “A METHOD OF INDUCING A CTL RESPONSE”.

Various parameters can be taken into account in delivering or administering an immunogenic composition to a subject. In addition, a dosage regimen and immunization schedule may be employed. Generally the amount of the components in the therapeutic composition will vary from patient to patient and from antigen to antigen, depending on such factors as: the activity of the antigen in inducing a response; the flow rate of the lymph through the patient's system; the weight and age of the subject; the type of disease and/or condition being treated; the severity of the disease or condition; previous or concurrent therapeutic interventions; the capacity of the individual's immune system to synthesize antibodies; the degree of protection desired; the manner of administration and the like, all of which can be readily determined by the practitioner.

In general the therapeutic composition may be delivered at a rate of from about 1 to about 500 microliters/hour or about 24 to about 12000 microliters/day. The concentration of the antigen is such that about 0.1 micrograms to about 10,000 micrograms of the antigen will be delivered during 24 hours. The flow rate is based on the knowledge that each minute approximately about 100 to about 1000 microliters of lymph fluid flows through an adult inguinal lymph node. The objective is to maximize local concentration of vaccine formulation in the lymph system. A certain amount of empirical investigation on patients will be necessary to determine the most efficacious level of infusion for a given vaccine preparation in humans.

In particular embodiments, the immunogenic composition of the present invention may be administered as a number of sequential doses. Such doses may be 2, 3, 4, or more doses as is needed to obtain the appropriate immune response. In further embodiments of the present invention, it is contemplated that the doses of the immunogenic composition would be administered within about seconds or minutes of each other into the right or left inguinal lymph nodes. For example, the plasmid (prime) may first be injected into the right lymph node followed within seconds or minutes by a second plasmid into the right or left inguinal lymph nodes. In other instances the combination of one or more plasmid expressing one or more immunogens may be administered. It is preferred that the subsequent injection following the first injection into the lymph node be within at about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more minutes but not greater than about 30, 40, 50, or 60 minutes of the first injection. Similar considerations apply to the administration of two peptides individually to the right and left lymph nodes. It may be desirable to administer the doses of the immunogenic composition of the invention at an interval of days, where several days (1, 2, 3, 4, 5, 6, or 7, or more days) lapse between subsequent administrations. In other instances it may be desirable for subsequent administration(s) of the compositions of the invention to be administered via bilateral inguinal lymph node injection within about 1, 2, 3, or more weeks or within about 1, 2, 3, or more months following the initial dose administration.

Administration may be in any manner compatible with the dosage formulation and in such amount as will be therapeutically effective. An effective amount or dose of an immunogenic composition of the present invention is that amount needed to provide a desired response in the subject to be treated.

In addition to those already disclosed in this application, the following applications are hereby expressly incorporated by reference in their entireties. Useful methods for using the disclosed analogs in inducing, entraining, maintaining, modulating and amplifying class I MHC-restricted T cell responses, and particularly effector and memory CTL responses to antigen, are described in U.S. Pat. Nos. 6,994,851 (Feb. 7, 2006) and 6,977,074 (Dec. 20, 2005) both entitled “A Method of Inducing a CTL Response”; U.S. Provisional Application No. 60/479,393, filed on Jun. 17, 2003, entitled “METHODS TO CONTROL MHC CLASS I-RESTRICTED IMMUNE RESPONSE”; and U.S. patent application Ser. No. 10/871,707 (Pub. No. 2005 0079152) and Provisional U.S. Patent Application No. 60/640,402 filed on Dec. 29, 2004, both entitled “Methods to elicit, enhance and sustain immune responses against MHC class I-restricted epitopes, for prophylactic or therapeutic purpose”. The analogs can also be used in research to obtain further optimized analogs. Numerous housekeeping epitopes are provided in U.S. application Ser. Nos. 10/117,937, filed on Apr. 4, 2002 (Pub. No. 20030220239 A1), and 10/657,022 (20040180354), and in PCT Application No. PCT/US2003/027706 (Pub. No. WO04022709A2), filed on Sep. 5, 2003; and U.S. Provisional Application Nos. 60/282,211, filed on Apr. 6, 2001; 60/337,017, filed on Nov. 7, 2001; 60/363,210 filed on Mar. 7, 2002; and 60/409,123, filed on Sep. 5, 2002; each of which applications is entitled “Epitope Sequences”. The analogs can further be used in any of the various modes described in those applications. Epitope clusters, which may comprise or include the instant analogs, are disclosed and more fully defined in U.S. patent application Ser. No. 09/561,571, filed on Apr. 28, 2000, entitled EPITOPE CLUSTERS. Methodology for using and delivering the instant analogs is described in U.S. patent application Ser. Nos. 09/380,534 and 6977074 (Issued Dec. 20, 2005) and in PCT Application No. PCTUS98/14289 (Pub. No. WO9902183A2), each entitled A “METHOD OF INDUCING A CTL RESPONSE”. Beneficial epitope selection principles for such immunotherapeutics are disclosed in U.S. patent application Ser. No. 09/560,465, filed on Apr. 28, 2000, Ser. No. 10/026,066 (Pub. No. 20030215425 A1), filed on Dec. 7, 2001, and Ser. No. 10/005,905 filed on Nov. 7, 2001, all entitled “Epitope Synchronization in Antigen Presenting Cells”; U.S. Pat. No. 6,861,234 (issued 1 Mar. 2005; application Ser. No. 09/561,074), entitled “Method of Epitope Discovery”; Ser. No. 09/561,571, filed Apr. 28, 2000, entitled EPITOPE CLUSTERS; Ser. No. 10/094,699 (Pub. No. 20030046714 A1), filed Mar. 7, 2002, entitled “Anti-Neovasculature Preparations for Cancer”; application Ser. Nos. 10/117,937 (Pub. No. 20030220239 A1) and PCTUS02/11101 (Pub. No. WO02081646A2), both filed on Apr. 4, 2002, and both entitled “EPITOPE SEQUENCES”; and application Ser. Nos. 10/657,022 and PCT Application No. PCT/US2003/027706 (Pub. No. WO04022709A2), both filed on Sep. 5, 2003, and both entitled “EPITOPE SEQUENCES”. Aspects of the overall design of vaccine plasmids are disclosed in U.S. patent application Ser. No. 09/561,572, filed on Apr. 28, 2000, entitled “Expression Vectors Encoding Epitopes of Target-Associated Antigens” and 10/292,413 (Pub. No. 20030228634 A1), filed on Nov. 7, 2002, entitled “Expression Vectors Encoding Epitopes of Target-Associated Antigens and Methods for their Design”; 10/225,568 (Pub No. 2003-0138808), filed on Aug. 20, 2002, PCT Application No. PCT/US2003/026231 (Pub. No. WO 2004/018666), filed on Aug. 19, 2003, both entitled “EXPRESSION VECTORS ENCODING EPITOPES OF TARGET-ASSOCIATED ANTIGENS”; and U.S. Pat. No. 6,709,844, entitled “AVOIDANCE OF UNDESIRABLE REPLICATION INTERMEDIATES IN PLASMID PROPAGATION”. Specific antigenic combinations of particular benefit in directing an immune response against particular cancers are disclosed in Provisional U.S. patent Application No. 60/479,554, filed on Jun. 17, 2003 and U.S. patent application Ser. No. 10/871,708, filed on Jun. 17, 2004 and PCT Patent Application No. PCT/US2004/019571 (Pub. No. WO 2004/112825), all entitled “Combinations of tumor-associated antigens in vaccines for various types of cancers”. Antigens associated with tumor neovasculature (e.g., PSMA, VEGFR2, Tie-2) are also useful in connection with cancerous diseases, as is disclosed in U.S. patent application Ser. No. 10/094,699 (Pub. No. 20030046714 A1), filed Mar. 7, 2002, entitled “Anti-Neovasculature Preparations for Cancer”. Methods to trigger, maintain, and manipulate immune responses by targeted administration of biological response modifiers are disclosed U.S. Provisional Application No. 60/640,727, filed on Dec. 29, 2004. Methods to bypass CD4+ cells in the induction of an immune response are disclosed in U.S. Provisional Application No. 60/640,821, filed on Dec. 29, 2004. Exemplary diseases, organisms and antigens and epitopes associated with target organisms, cells and diseases are described in U.S. Application No. 6977074 (issued Dec. 20, 2005) filed Feb. 2, 2001 and entitled “METHOD OF INDUCING A CTL RESPONSE”. Exemplary methodology is found in U.S. Provisional Application No. 60/580,969, filed on Jun. 17, 2004, and U.S. Patent Application No. 2006-0008468-A1, published on Jan. 12, 2006, both entitled “COMBINATIONS OF TUMOR-ASSOCIATED ANTIGENS IN DIAGNOTISTICS FOR VARIOUS TYPES OF CANCERS”. Methodology and compositions are also disclosed in U.S. Provisional Application No. 60/640,598, filed on Dec. 29, 2004, entitled “COMBINATIONS OF TUMOR-ASSOCIATED ANTIGENS IN COMPOSITIONS FOR VARIOUS TYPES OF CANCER”. The integration of diagnostic techniques to assess and monitor immune responsiveness with methods of immunization including utilizing the instant analogs is discussed more fully in Provisional U.S. Patent Application No. 60/580,964 filed on Jun. 17, 2004 and U.S. Patent Application No. US-2005-0287068-A1, published on Dec. 29, 2005) both entitled “Improved efficacy of active immunotherapy by integrating diagnostic with therapeutic methods”. The immunogenic polypeptide encoding vectors are disclosed in U.S. patent application Ser. No. 10/292,413 (Pub. No. 20030228634 A1), filed on Nov. 7, 2002, entitled Expression Vectors Encoding Epitopes of Target-Associated Antigens and Methods for their Design, and in U.S. Provisional Application No. 60/691,579, filed on Jun. 17, 2005, entitled “Methods and compositions to elicit multivalent immune responses against dominant and subdominant epitopes, expressed on cancer cells and tumor stroma”. Additional useful disclosure, including methods and compositions of matter, is found in U.S. Provisional Application No. 60/691,581, filed on Jun. 17, 2005, entitled “Multivalent Entrain-and-Amplify Immunotherapeutics for Carcinoma”. Further methodology, compositions, peptides, and peptide analogs are disclosed in U.S. Provisional Application Nos. 60/581,001 and 60/580,962, both filed on Jun. 17, 2004, and respectively entitled “SSX-2 PEPTIDE ANALOGS” and “NY-ESO PEPTIDE ANALOGS.” Each of the applications and patents mentioned in the above paragraphs is hereby incorporated by reference in its entirety for all that it teaches. Additional analogs, peptides and methods are disclosed in U.S. Patent Application Publication No 20060063913, entitled “SSX-2 PEPTIDE ANALOGS”; and U.S. Patent Publication No. 2006-0057673 A1, published on Mar. 16, 2006, entitled “EPITOPE ANALOGS”; and PCT Application Publication No. WO/2006/009920, entitled “EPITOPE ANALOGS”; all filed on Jun. 17, 2005. Further methodology and compositions are disclosed in U.S. Provisional Application No. 60/581,001, filed on Jun. 17, 2004, entitled “SSX-2 PEPTIDE ANALOGS”, and to U.S. Provisional Application No. 60/580,962, filed on Jun. 17, 2004, entitled “NY-ESO PEPTIDE ANALOGS”; each of which is incorporated herein by reference in its entirety. As an example, without being limited thereto each reference is incorporated by reference for what it teaches about class I MHC-restricted epitopes, analogs, the design of analogs, uses of epitopes and analogs, methods of using and making epitopes, and the design and use of nucleic acid vectors for their expression. Other applications that are expressly incorporated herein by reference are: U.S. patent application Ser. No. 11/156,253 (Publication No. 20060063913), filed on Jun. 17, 2005, entitled “SSX-2 PEPTIDE ANALOGS”; U.S. patent application Ser. No. 11/155,929, filed on Jun. 17, 2005, entitled “NY-ESO-1 PEPTIDE ANALOGS” (Publication No. 20060094661); U.S. patent application Ser. No. 11/321,967, filed on Dec. 29, 2005, entitled “METHODS TO TRIGGER, MAINTAIN AND MANIPULATE IMMUNE RESPONSES BY TARGETED ADMINISTRATION OF BIOLOGICAL RESPONSE MODIFIERS INTO LYMPHOID ORGANS”; U.S. patent application Ser. No. 11/323,572, filed on Dec. 29, 2005, entitled “METHODS TO ELICIT ENHANCE AND SUSTAIN IMMUNE REPONSES AGAINST MCH CLASS I RESTRICTED EPITOPES, FOR PROPHYLACTIC OR THERAPEUTIC PURPOSES”; U.S. patent application Ser. No. 11/323,520, filed Dec. 29, 2005, entitled “METHODS TO BYPASS CD4+ CELLS IN THE INDUCTION OF AN IMMUNE RESPONSE”; U.S. patent application Ser. No. 11/323,049, filed Dec. 29, 2005, entitled “COMBINATION OF TUMOR-ASSOCIATED ANTIGENS IN COMPOSITIONS FOR VARIOUS TYPES OF CANCERS”; U.S. patent application Ser. No. 11,323,964, filed Dec. 29, 2005, entitled “COMBINATIONS OF TUMOR-ASSOCIATED ANTIGENS IN DIAGNOSTICS FOR VARIOUS TYPES OF CANCERS”; U.S. Provisional Application Ser. No. 60/691,889, filed on Jun. 17, 2005 entitled “EPITOPE ANALOGS.”

VI. Examples

The following examples are included to demonstrate preferred embodiments of the invention in designing plasmids containing immunogenic epitopes of PSMA and PRAME that are capable of eliciting a bivalent immune response. It should be appreciated by those of skill in the art that the methodology disclosed in the examples which follow represent methodologies discovered by the inventors to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.

Example 1 Design of Plasmid Expression Vectors Encoding Immunogens

The plasmids P2 and R2 (also referred to as pCTLR2) contain elements from PSMA (expressed on the neovasculature of a wide range of carcinomas or by prostate carcinoma cells) and PRAME (expressed by cancerous cells), respectively, (FIG. 1). Each insert encompasses a fragment of the antigen's sequence along with multiple copies of an epitope expressed by target cells and addressable via immune mediated attack. Flanking these epitopes are sequences encoding amino acids known to facilitate the processing and generation of epitope peptides in the cellular compartments. In addition, plasmid RP5 encompasses elements from both P2 and R2 with the expressed immunogens adjoined to each other.

The R2 plasmid was constructed following the plasmid construction protocol discussed above and as disclosed in U.S. Provisional Patent Application No. 60/691,889, filed on Jun. 17, 2005 entitled EPITOPE ANALOGS; and U.S. patent application Ser. No. 11/455,278 entitled PRAME EPITOPE ANALOGS, incorporated herein by reference in its entirety. R2, also referred to as pCTLR2, is a recombinant DNA plasmid vaccine which encodes one polypeptide with an HLA A2-specific CTL epitope from PRAME, SLLQHLIGL (SEQ ID NO:5), amino acid residues 425-433, and an epitope cluster region of PRAME, amino acids 422-509 (SEQ ID NO:21). In constructing this plasmid, the DNA sequence encoding the polypeptide in the plasmid is placed under the control of promoter/enhancer sequence from cytomegalovirus (CMVp) which allows efficient transcription of messenger for the polypeptide upon uptake by antigen presenting cells. A bovine growth hormone polyadenylation signal (BGH polyA) at the 3′ end of the encoding sequence provides signal for polyadenylation of the messenger to increase its stability as well as translocation out of nucleus into the cytoplasm. To facilitate plasmid transport into the nucleus, a nuclear import sequence (NIS) from Simian virus 40 has been inserted in the plasmid backbone. One copy of CpG immunostimulatory motif is engineered into the plasmid to further boost immune responses. Additionally, two prokaryotic genetic elements in the plasmid are responsible for amplification in E. coli, the kanamycin resistance gene (Kan R) and the pMB bacterial origin of replication.

The amino acid sequence (SEQ ID NO:10) of the encoded polypeptide of R2 (pCTLR2) is 150 amino acid residues in length as shown below:

malqsllqhliglsnithylypvplesyedihgtlhlerlaylharlrellcelgrpsmvwlsanpcphcgdrtfydpepilcpcfmpnkrsllqhliglgdaaysllqhliglispekeeqyiasllqhliglkrpsikrsllqhligl

Amino acid residues 2 to 89 correspond to an epitope cluster region representing PRAME₄₂₂₋₅₀₉ (SEQ ID NO:21). Within this epitope cluster region, a number of potential HLA A2-specific CTL epitopes have been found using a variety of epitope prediction algorithms. Amino acid residues 90-150 are an epitope liberation (Synchrotope™) sequence with four embedded copies of the PRAME₄₂₅₋₄₃₃ (SEQ ID NO:5) CTL epitope (boldface). Flanking the defined PRAME CTL epitope are short amino acid sequences that have been shown to play an important role in the processing of the PRAME CTL epitope. In addition, the amino acid sequence ISPEKEEQYIA (SEQ ID NO: 28; corresponding to PRAME amino acid 276-286, in italics) is engineered into this string-of-beads region to facilitate the antibody-based detection of expression of encoded polypeptide.

Example 2 Dominant/Subdominant Hierarchy of Engineered Immunogenic Elements

A study was conducted to assess whether the strategy of engineering elements from different antigens into the same expression vector creates a dominant/subdominant hierarchy amongst those elements.

Four groups of HHD transgenic mice were immunized with plasmids P2, R2, RP5 or a mixture of P2 and R2 plasmids, by direct inoculation into the inguinal lymph nodes of 25 μg/plasmid in 25 μl of PBS to each lymph node at day 1, 4, 15 and 18. Ten days after the boost, splenocytes were stimulated ex vivo with PRAME₄₂₅₋₄₃₃ (SEQ ID NO:5) or PSMA₂₈₈₋₂₉₇ (SEQ ID NO:6) peptide and tested against ⁵¹Cr-labeled peptide coated-T2 cells, at various effector to target cell ratios (E:T ratio).

Briefly, target cells expressing antigen on their surface were labeled with a radioactive isotope of chromium (⁵¹Cr). Splenocytes were then mixed with the target cell and incubated for several hours. After incubation, supernatants were harvested and the cytolytic activity was measured in triplicate samples using a gamma counter. Lysis of antigen-expressing cells releases ⁵¹Cr into the medium. Cell-specific lysis is calculated by comparing lysis (i.e., chromium release) of target cells expressing the antigen(s) of interest or control antigen(s) in the presence or absence of effector cells, and is usually expressed as the % specific lysis.

The corrected percent lysis was calculated for each concentration of effector cells, using the mean cpm for each replicate of wells (FIG. 2). Percent specific lysis was calculated using the following formula: Percent release=100× (Experimental release−spontaneous release)/(Maximum release−spontaneous release). Data are presented as follows: the x-axis shows the effector to target ratio; the y-axis shows the corresponding percentage specific lysis. Results are expressed as % specific cytotoxicity (the plasmid R2 is also referred to a CTLR2).

The results show that P2 and R2 separately elicit significant cytotoxic immune responses. However, when the immunogens of P2 and R2 are integrated within the RP5 plasmid, immunity against the PRAME epitope is preserved while response to PSMA₂₈₈₋₂₉₇ (SEQ ID NO:6) epitope is eclipsed. This indicates that from an immunological standpoint a hierarchy is established between these two epitopes. Admixing P2 and R2 plasmids restores bivalent immunity.

Example 3 Structure of Additional Plasmids

To design expression vectors that result in a more balanced immunity against both PRAME and PSMA epitopes (dominant and subdominant in the context of RP5), a set of immunogens was designed and incorporated within the same plasmid backbone by employing various combinations of the three following methods:

-   -   1) The ratio between the copy numbers of the PRAME₄₂₅₋₄₃₃ (SEQ         ID NO:5) (dominant) epitope and that of the PSMA₂₈₈₋₂₉₇         (subdominant) epitope was adjusted in favor of the latter.     -   2) The less dominant epitope was placed in the C terminal         position so that it would have the proper C-terminus independent         of proteasomal processing.     -   3) The less dominant epitope (PSMA) was mutated (one or multiple         copies within the expressed insert) to improve intrinsic         immunogenic properties such as binding to, and half-life on,         class I MHC.

FIG. 3 shows the design of the various plasmids made. In FIG. 3, “V” corresponds to PSMA₂₆₆₋₂₉₇ (SEQ ID NO:29) epitopes that carry an I297V mutation.

Example 4 Induction of Bivalent Responses Achieved by Plasmids Encompassing Epitopes from Different Antigens

The plasmids designed as described in Example 3 above, were tested to determine their ability to prime a bivalent immune response against the PRAME₄₂₅₋₄₃₃ (SEQ ID NO:5) and PSMA₂₈₈₋₂₉₇ (SEQ ID NO:6) tumor associated antigens.

Six groups of HHD transgenic mice (n=8/group) were immunized with plasmids (RP8, RP9, RP10, RP11, RP12, or RP13) carrying inserts depicted in FIG. 3, by direct inoculation into the inguinal lymph nodes of 25 μg in 25 μl of PBS to each lymph node on day 1 and 4. Seven days after the last plasmid injection, on day 11, all of the immunized animals were sacrificed including five naive controls. ELISPOT analysis was conducted by measuring the frequency of IFN-γ producing spot forming colonies (SFC), as described below.

Briefly, spleens were isolated on day 11 from euthanized animals and the mononuclear cells, after density centrifugation (Lympholyte Mammal, Cedarlane Labs, Burlington, N.C.), were resuspended in HL-1 medium. Splenocytes (5×10⁵ or 2.5×10⁵ cells per well) were incubated with 10 μg of PSMA₂₈₈₋₂₉₇ (SEQ ID NO:6) or PRAME₄₂₅₋₄₃₃ (SEQ ID NO:5), natural peptide in triplicate wells of a 96 well filter membrane plates (Multi-screen IP membrane 96-well plate, Millipore, Mass.). Samples were incubated for 42 hours at 37° C. with 5% CO₂ and 100% humidity prior to development. Mouse IFN-γ coating antibody (IFN-γ antibody pair, U-CyTech Biosciences, The Netherlands) was used as a coating reagent prior to incubation with splenocytes, followed by the accompanied biotinylated detection antibody. GABA conjugate and proprietary substrates from U-CyTech Biosciences were used for IFN-γ spot development. The CTL response in immunized animals was measured 24 hours after development on the AID International plate reader using ELISpot Reader software version 3.2.3 calibrated for IFN-γ spot analysis.

The results depicted in FIG. 4 show the average IF′N-γ spot count for each experimental group. The data are presented as the frequency of IF′N-γ spots (representing a colony of IFN-γ secreting cells) per treatment, as the average of individual animal responses +/− the standard deviation (Std). Data generated from splenocytes isolated from immunized or naive mice and stimulated with the PSMA₂₈₈₋₂₉₇ native peptide indicated that RP12 induced the strongest immunity to the PSMA₂₈₈₋₂₉₇ antigen (55.8+/−1.6 INF-γ spots) as compared to the naive control (12.8+2.4 IFN-γ spots) or the other treatment groups. This represented a 5-fold enhanced PSMA immune response with the RP12 plasmid.

In addition, data generated from splenocytes isolated from immunized or naive mice and stimulated with the PRAME₄₂₅₋₄₃₃ native peptide also demonstrated that animals immunized with RP12 showed the strongest immune response to the PRAME₄₂₅₋₄₃₃ antigen (234.5+3.7 IFN-γ spots) as compared to the naive controls (8.5+2.8 IFN-γ spots) or the other treatment groups. This represented a greater than 20-fold increased PRAME response with the RP12 plasmid.

Overall, the results depicted in FIG. 4 show induction of a strong bivalent immunity against both PRAME and PSMA epitopes by the plasmid RP12. Some bivalent immunity against both PRAME and PSMA epitopes was observed with RP9 and to a lesser extent RP13, RP10, RP11 and RP8—all having a more potent representation of the PSMA epitope relative to PRAME epitope as compared to the plasmid RP5 (FIG. 2). This observation is apparently due in part to use of the I297V analogue of PSMA.

Example 5 Induction of a Bivalent Response by the RP12 Plasmid

Based on the comparison in Example of 4 of the six plasmids (RP8, RP9, RP10, RP11, RP12, and RP13), RP12 was selected for further analysis, as it was the only plasmid that primed a robust, bivalent immune response against both PRAME₄₂₅₋₄₃₃ (SEQ ID NO:5) and PSMA₂₈₈₋₂₉₇ (SEQ ID NO:6).

Two representative HHD transgenic mice were immunized with RP12 plasmid carrying an insert (depicted in FIG. 3) by direct inoculation into the inguinal lymph nodes of 25 μg in 25 μl of PBS to each lymph node at day 1, 4, 15 and 18. Ten days after the last plasmid injection, the frequency of PRAME and PSMA epitope-specific CD8⁺ T cells was measured by tetramer staining of peripheral blood mononuclear cells and co-staining for CD8 expression.

Briefly, mononuclear cells were isolated from peripheral blood after density centrifugation (Lympholyte Mammal, Cedarlane Labs) and stained with HLA-A*0201 PRAME MHC tetramer (Beckman Coulter, T02001), and HLA-A*0201 PSMA MHC tetramer (Beckman Coulter, T02001). These cells were then co-stained using FITC conjugated rat anti-mouse CD8a (Ly-2) monoclonal antibody (BD Biosciences, 553031). Data were collected using a BD FACS Calibur flow cytometer and analyzed using Cellquest software by gating on the lymphocyte population and calculating the percent of tetramer positive cells within the CD8′ CTL population.

The results depicted in FIG. 5, show that following intranodal plasmid immunization, the RP12 plasmid elicited dual immunity and the frequency of PRAME₄₂₅₋₄₃₃ specific T cells was several fold higher than that of T cells specific for the PSMA subdominant epitope

Example 6 Bivalent Immune Response in Mice Primed with PRAME and PSMA Plasmid and Boosted with Peptide

To determine whether immunization with the plasmids RP12 and RP8 could induce a bivalent response against the tumor associated antigens Prame₄₂₅₋₄₃₃ and PSMA₂₈₈₋₂₉₇, following peptide boost with the PSMA₂₈₈₋₂₉₇ I297V (SEQ ID NO:7) analogue, a tetramer analysis of immunized animals was conducted.

HHD transgenic mice were immunized with RP8 or RP12 plasmids carrying inserts depicted in FIG. 3, by direct inoculation into the inguinal lymph nodes of 100 μg in 25 μl of PBS to each lymph node at day 1, 4, 15 and 18. On days 29 and 32, the mice were boosted with 25 μg of PSMA₂₈₈₋₂₉₇ peptide analogue (I297V). One day before initiation of peptide boost and ten days after the completion of plasmid boost, the frequency of PRAME and PSMA epitope-specific T cells was measured by tetramer staining (as described above) and compared to tetramer results seven days following the last peptide boost.

The results shown in FIG. 6, as mean±SEM of specific CD8⁺T cell frequency showed that RP12 plasmid elicits a slightly higher PSMA-specific immunity than RP8 prior to peptide boost. In addition, in both the case of RP12 and RP8, the immunity against PRAME was found to be dominant prior to peptide boost. However, after boost with the PSMA subdominant epitope, the immune response against PRAME and PSMA displayed a more balanced profile, particularly in the case of RP12, indicating the benefit of strategies to elicit equilibrated immune responses against epitopes of different immune hierarchy.

FIG. 6B shows immune responses to PRAME and PSMA in three representative mice from each group and further illustrate the enhanced bivalent response elicited by the RP12 plasmid and the PSMA (I297V) peptide boost.

Example 7 Bivalent Immune Response after PSMA Peptide Boost and Subsequent PRAME Peptide Boost

It was examined whether immunization with the plasmids RP12 and RP8 could induce a bivalent response against the PRAME₄₂₅₋₄₃₃ (SEQ ID NO:5) and PSMA₂₈₈₋₂₉₇ (SEQ ID NO:6) epitopes those tumor associated antigens, following a first peptide boost with the PSMA₂₈₈₋₂₉₇ I297V (SEQ ID NO:7) analogue and a second boosting with PRAME₄₂₅₋₄₃₃ L426Nva, L433Nle (SEQ ID NO:30) peptide analogue.

Mice were immunized with 4 injections of the RP8 or RP12 plasmid (4 mg/ml) by direct inoculation into the inguinal lymph nodes at day 1, 4, 15 and 18. On days 29 and 32, the mice were boosted with PSMA₂₈₈₋₂₉₇ I297V peptide analogue (0.5 mg/ml), followed by a second boost on day 42 and 59 with Prame₄₂₅₋₄₃₃ L426Nva, L433Nle peptide analogue at 0.5 mg/ml and 0.05 mg/ml respectively. Mice were sacrificed and an ELISPOT analysis (FIG. 7) was conducted as follows.

Briefly, spleens were isolated ten days following the last Prame₄₂₅₋₄₃₃ L426Nva, L433Nle peptide injection from euthanized animals and the mononuclear cells, after density centrifugation (Lympholyte Mammal, Cedarlane Labs, Burlington, N.C.), were resuspended in HL-1 medium. Splenocytes (2×10⁵ cells per well) were incubated with 10 μg of PSMA₂₈₈₋₂₉₇ or PRAME₄₂₅₋₄₃₃, natural peptide in triplicate wells of a 96 well filter membrane plates (Multi-screen IP membrane 96-well plate, Millipore, Mass.). Samples were incubated for 72 hours at 37° C. with 5% CO₂ and 100% humidity prior to development. Mouse IFN-γ coating antibody (IFN-γ antibody pair, U-CyTech Biosciences, The Netherlands) was used as a coating reagent prior to incubation with splenocytes, followed by the accompanied biotinylated detection antibody. GABA conjugate and various substrates from U-CyTech Biosciences were used for IFN-γ spot development. The CTL response in immunized animals was measured 24 hours after development on the AID International plate reader using ELISpot Reader software version 3.2.3 calibrated for IFN-γ spot analysis.

The results show that RP12 plasmid elicits a higher PSMA-specific immunity than RP8 at all doses tested. For both the RP12 and RP8 plasmids, the immunity against PRAME was found to be dominant at all doses tested. Also, the RP12 plasmid showed a strong balanced immune response against PRAME and PSMA following boost with the PSMA and PRAME epitopes. 

What is claimed:
 1. An engineered nucleic acid construct encoding a polypeptide comprising an array of epitopes, wherein the array comprises one or more copies of CTL epitope PSMA₂₈₈₋₂₉₇ (SEQ ID NO:6), or a cross-reactive analogue differing from SEQ ID NO:6 by only 1-3 substitutions, and one or more copies of CTL epitope PRAME₄₂₅₋₄₃₃ (SEQ ID NO:5), or a cross-reactive analogue differing from SEQ ID NO:5 by only 1-3 substitutions, wherein the polypeptide does not comprise a whole PSMA antigen (SEQ ID NO: 19), and wherein the polypeptide does not comprise a whole PRAME antigen (SEQ ID NO: 20).
 2. The nucleic acid construct of claim of 1, wherein one or both epitopes are encoded within a liberation sequence.
 3. The nucleic acid construct of claim 1, wherein said polypeptide further comprises a sequence encoding one or more epitope clusters.
 4. The nucleic acid construct of claim 3 comprising a PRAME epitope cluster.
 5. The nucleic acid construct of claim 4, wherein said epitope cluster consists essentially of amino acids 422-509 of PRAME (SEQ ID NO:21).
 6. The nucleic acid construct of claim 3 comprising a PSMA epitope cluster.
 7. The nucleic acid construct of claim 6, wherein said epitope cluster is chosen from the group consisting of amino acids 3-45 of PSMA (SEQ ID NO:22) and 217-297 of PSMA (SEQ ID NO:23).
 8. The nucleic acid construct of claim 1, wherein the cross-reactive analogue of CTL epitope PSMA₂₈₈₋₂₉₇ (SEQ ID NO:6) comprises a I297V substitution.
 9. The nucleic acid construct of claim 1 further comprising a nuclear import sequence.
 10. The nucleic acid construct of claim 1 further comprising one or more of a CpG immunostimulatory motif.
 11. The nucleic acid construct of claim 2, wherein the liberation sequence of the PRAME and PSMA epitope is located in the N-terminal portion of the encoded polypeptide.
 12. The nucleic acid construct of claim 2, wherein the encoded polypeptide is SEQ ID NO:
 2. 13. The nucleic acid construct of claim 2, wherein the liberation sequence of the PRAME and PSMA epitopes is located in the C-terminal portion of the encoded polypeptide.
 14. The nucleic acid construct of claim 13, wherein the encoded polypeptide is SEQ ID NO:
 4. 15. An immunogenic composition comprising the nucleic acid construct of claim
 1. 16. The nucleic acid construct of claim of 2, wherein both epitopes are encoded within a liberation sequence.
 17. The nucleic acid construct of claim 1, wherein the array comprises a flanking amino acid sequence adjacent to a PSMA₂₈₈₋₂₉₇ epitope for liberation of the epitope by immunoproteasome processing.
 18. The nucleic acid construct of claim 1, wherein the array comprises a flanking amino acid sequence adjacent to a PRAME₄₂₅₋₄₃₃ epitope for liberation of the epitope by immunoproteasome processing.
 19. The nucleic acid construct of claim 17, wherein the flanking amino acid sequence is not an epitope.
 20. The nucleic acid construct of claim 18, wherein the flanking amino acid sequence is not an epitope.
 21. The nucleic acid construct of claim 19, wherein the flanking amino acid sequence is at least 2 amino acids in length.
 22. The nucleic acid construct of claim 20, wherein the flanking amino acid sequence is at least 2 amino acids in length.
 23. The nucleic acid construct of claim 1 further comprising a promoter.
 24. The nucleic acid construct of claim 23, wherein the promoter is a cytomegalovirus (CMV) promoter.
 25. The nucleic acid construct of claim 1 further comprising a poly A sequence. 